Zn (Zinc) deficiency triggers ‘hidden hunger’. Enhancing Zn concentration in wheat grains and Zn fertilizer use efficiency through biofortification can effectively increase dietary Zn intake, thereby improving human Zn nutritional status.

The study subjects were two distinctive colored-grain wheat varieties: ‘Taihei 5’ (purple-grained) and ‘Tailan 8’ (blue-grained). A two-year field experiment was conducted from 2022-2024 in Taigu District, Jinzhong City, Shanxi Province. Foliar Zn application was performed at 3-5 days after the flowering of colored-grain wheat (Over 50% of spikes in the wheat field had lemma and palea separation at middle-upper florets while anthers were dehiscing). Five Zn concentration treatments were applied: Zn0 (deionized water), Zn1 (Zn concentration: 440 mg·L^-1), Zn2 (Zn concentration: 587 mg·L^-1), Zn3 (Zn concentration: 733 mg·L^-1), Zn4 (Zn concentration: 880 mg·L^-1). Through analysis of grain yield and Zn concentrations in grains, leaves, and stems across multiple post-anthesis periods for both colored-grain wheat types, Zn concentration variation dynamics, Zn accumulation and partitioning characteristics, Zn utilization efficiency, grain Zn biofortification index and grain Zn harvest indices were quantitatively analyzed to evaluate their Zn biofortification efficacy.

Foliar Zn application significantly increased Zn concentrations in all organs and grain yield of colored-grain wheat, The Zn3 treatment produced the highest grain Zn concentration (21.79-67.90 mg·kg^-1) and peak grain yield (4937.36-5097.27 kg·hm^-2). Grain Zn accumulation reached its optimum (251.30-301.54 g·hm^-2) under the Zn3 treatment, while Zn concentrations and accumulation in leaves and stems increased linearly with rising application concentrations. With increasing Zn application concentrations, the grain Zn accumulation proportion showed a declining trend (10%-18%), while the leaf Zn accumulation proportion rose to 66%, and stem Zn accumulation remained at 23%-30%. Furthermore efficient synergy in Zn utilization efficiency across all organs of colored-grain wheat was achieved under Zn3 treatment (5.68%-7.70%). With increasing Zn application concentrations, the grain Zn biofortification index and Zn harvest index declined. Compared with Zn1, other Zn treatments reduced the grain Zn biofortification index by 12.50%-47.02%, while relative to the control (Zn0), all Zn treatments decreased the Zn harvest index by 23.66%-60.44%. ‘Taihei 5’ outperformed ‘Tailan 8’ in grain Zn concentration, accumulation, utilization efficiency, and biofortification performance. Possibly influenced by precipitation, both types of colored-grain wheat performed better in the second growing season

Post-anthesis foliar Zn application effectively regulated Zn accumulation and partitioning in colored-grain wheat. The combination of purple-grained wheat varieties and foliar Zn application at 733 mg·L^-1 achieved the optimal balance between grain Zn concentration and Zn utilization efficiency in colored-grain wheat systems.